Arrays

An array holds many values under one name. In PHP an array is an ordered map: every value has a key, and the order you add items is kept. That single structure works as a list, a dictionary or a stack.

Indexed arrays

When you do not give keys, PHP numbers the items from 0:

PHP

<?php

$languages = ['PHP', 'JavaScript', 'Python'];

echo $languages[0];       // PHP
echo $languages[2];       // Python
echo count($languages);   // 3

Indexes start at 0, so the last item of an array with three elements is at index 2. Trying to read $languages[3] gives a warning and null.

Associative arrays

Give each value a meaningful key when position does not mean anything:

PHP

<?php

$user = [
    'name' => 'Asha',
    'email' => 'asha@example.com',
    'posts' => 42,
];

echo $user['name'];                                    // Asha
echo "{$user['name']} has written {$user['posts']} posts.";

Keys can be strings or integers. Values can be anything, including other arrays.

Adding, updating and removing

PHP

<?php

$cart = ['apple', 'bread'];

$cart[] = 'milk';          // Append: ['apple', 'bread', 'milk']
$cart[0] = 'green apple';  // Update by index

$user = ['name' => 'Asha'];
$user['role'] = 'editor';  // Add a new key

unset($user['role']);      // Remove a key
array_pop($cart);          // Remove and return the last item ('milk')
array_unshift($cart, 'eggs'); // Add to the start

Reading safely

Reading a key that does not exist raises a warning. Check first, or supply a default:

PHP

<?php

$settings = ['theme' => 'dark'];

$theme = $settings['theme'] ?? 'light';      // 'dark'
$language = $settings['language'] ?? 'en';   // 'en', no warning

var_dump(array_key_exists('theme', $settings)); // true
var_dump(isset($settings['language']));          // false
var_dump(in_array('dark', $settings, true));     // true: searches values

Pass true as the third argument of in_array() to compare strictly. Without it, in_array('1e1', ['10']) returns true.

isset() returns false for keys whose value is null; array_key_exists() returns true for them. Use array_key_exists() when null is a meaningful value.

Nested arrays

Arrays can contain arrays, which is how you represent lists of records:

PHP

<?php

$products = [
    ['name' => 'Notebook', 'price' => 3.50, 'stock' => 12],
    ['name' => 'Pen', 'price' => 1.20, 'stock' => 0],
    ['name' => 'Backpack', 'price' => 24.00, 'stock' => 3],
];

echo $products[2]['name']; // Backpack

foreach ($products as $product) {
    $status = $product['stock'] > 0 ? 'in stock' : 'sold out';
    echo "{$product['name']}: {$status}", PHP_EOL;
}

Sorting

Sorting functions change the array in place:

Function	Sorts by	Keeps keys?
`sort` / `rsort`	Value, ascending / descending	No, re-indexes
`asort` / `arsort`	Value	Yes
`ksort` / `krsort`	Key	Yes
`usort`	Your own comparison	No

PHP

<?php

$scores = ['Ben' => 72, 'Ada' => 91, 'Cy' => 85];

arsort($scores);
print_r($scores); // Ada 91, Cy 85, Ben 72

usort($products, fn($a, $b) => $a['price'] <=> $b['price']);
echo $products[0]['name']; // Pen (cheapest first)

The spaceship operator <=> returns -1, 0 or 1, exactly what usort expects.

Transforming arrays

These functions return a new array and leave the original unchanged:

PHP

<?php

$prices = [10, 25, 40];

$withVat = array_map(fn($p) => $p * 1.2, $prices);           // [12, 30, 48]
$expensive = array_filter($prices, fn($p) => $p > 20);       // [1 => 25, 2 => 40]
$total = array_sum($prices);                                  // 75

$names = array_column($products, 'name');                    // ['Pen', 'Notebook', 'Backpack']

fn($p) => ... is an arrow function: a short, one-expression function. You will meet functions properly in the next lesson.

array_filter() keeps the original keys, so the result above starts at key 1. Wrap it in array_values() when you need a clean 0, 1, 2 list.

Unpacking

Pull values out into variables in one step:

PHP

<?php

[$first, $second] = ['PHP', 'JavaScript'];
['name' => $name, 'email' => $email] = $user;

$all = [...$languages, 'Go']; // Spread one array into another

Summary

PHP arrays are ordered maps: indexed (keys 0, 1, 2) or associative (named keys).
Append with $array[] = value, remove with unset() or array_pop().
Read optional keys with ??; check with array_key_exists(), isset() or in_array(..., true).
Sort in place with sort, asort, ksort or usort.
Transform with array_map, array_filter, array_sum and array_column.

What you will learn

Before you start